Method for producing tubular radioactive light sources

ABSTRACT

According to the invention, the process for making tube-shaped, radioactive light sources is characterized by the fact that a glass tube containing a Luminophor and a radioactive gas, is subdivided successively into glass tube sections intended for use as radioactive light sources, by means of a laser beam. This is accomplished with a closely localized lazer beam so that a sufficient quantity of glass is drawn from the sidewalls to form end walls, to devide the sealed tube and simultaneously seal the ends of the two tubes produced without loss of radioactive gas therein.

Umted States Patent 1 1 3 Thuler 51 Dec. 19, 1972 [54] METHOD FORPRODUCING TUBULAR 3.203.779 8/1965 Reber Hes/10s RADIOACTIVE LIGHTSOURCES 3,453,097 7/1969 Hafner HUGS/112 3.460.930 8/l969 Pityo ..65/l55[72] Inventor: Oscar Thuler, Berne, Switzerland [73] Assignee: CanradPrecision Industries, Inc., 'f Exami7er S' Leon 1 New York NY AssistantExammerRobert L. Lindsay, .lr.

Attorney-Blum, Moscovitz. Friedman & Kaplan [22] Filed: June 11,1969

[211 App]. No.: 832,273 [57] ABSTRACT According to the invention, theprocess for making tube-shaped, radioactive light sources ischaracterized [30] Foreign Apphcauon Priority Data by the fact that aglass tube containing a Luminophor Aug. 22, 1968 Switzerland ..l2639/68and a radioactive gas, is subdivided successively into glass tubesections intended for use as radioactive light I52] [1.5. CI...65/l05.65/l l2, 65/I l3. sources, by means of a laser beam. This isaccom- 65/l55 plished with a closely localized lazer beam so that a [SiI Int. Cl. ..C03b 21/06 sufficient quantity of glass is drawn from thesidewalls [58] Field of Search ..65/36, I05. H2, 113, 269, to form endwalls, to devide the sealed tube and simul- 6S/l55.56, 57, 64 taneouslyseal the ends of the two tubes produced without loss of radioactive gastherein. [56] References Cited 6 Claims, 1 Drawing Figure UNITED STATESPATENTS 2,300,9l7 11/1942 Gaskill ..65/l05 PATENTEUW. w um METHOD FORPRODUCING TUBULAR RADIOACTIVE LIGHT SOURCES BACKGROUND FOR THE INVENTIONThere are known radioactive light sources, consisting of hollow, fusedglass bodies, which contains a Luminophor, for instance as an insidewall coating, or as filled-in particles, and a radioactive gas at alower pressure than atmospheric pressure. In this, the glass body mayhave the external shape of a pane (disc), of a flattened-out or acylindrical rod.

For producing such radioactive light sources, consisting of a glasstube, for instance a capillary tube, each glass tube filled with theLuminophor provided is connected to a vacuum source, evacuated, filledwith the radioactive gas to the pressure necessary and then fused with aflame.

Inasmuch as this process is inconvenient and timeconsuming, especiallyfor making very small light sources, that is, short capillary tubes, ithas been a desire of the industry to provide procedures to subdivide along glass tube containing the Luminophor and the radioactive gas bysectional fusion, i.e., by cutting the tube into sections with a flameinto individual tube sections. In following this concept, however,various and somewhat serious disadvantages have developed in pastprocedures.

One problem involved has been the control of the flame, that is, it isdifflcult to focus the flame sufficiently small, to turn the flame onand off in a simple manner in the shortest possible time, and to obtaina constant size of flame and flame temperature, especially immediatelyafter turning it on. Furthermore, a considerable disadvantage has beenfound by virtue of the fact that a dead zone of several millimeterslength has been formed at the hot, fused end of the capillary tube withrespect to the illumination power of the radioactive light source. Thisdead zone is produced by the excessive and too prolonged heating of theglass body, as the heat generated by the flame is not sufficient tocause fusion with sufficient speed, so that the heating of the glassbody is not localized only to the point which is to be melted. A furtherdisadvantage consists in the fact that, as a result of the unavoidablyintense heating of the glass body, the pressure of the radioactive gasrises greatly. Inasmuch as the pressure must remain below atmosphericpressure it is necessary to set a relatively low initial pressure beforestarting the fusion. This low gas pressure is again assumed, however, bythe fused light source after cooling. As the light intensity of theradioactive light source rises with the gas pressure, the light sourcefused in the manner described exhibits a relatively low and by no meansoptimal brightness.

DESCRIPTION OF THE DISCLOSURE This invention as delineated in theabstract is further explained by reference to the drawing whichillustrates in schematic form an example of construction and operationof an installation for carrying out the process according to theinvention which delineates a novel and effective mechanism and procedurefor effectuating the desired result.

DRAWING The FIGURE is a schematic front view of a device utilized inthis invention.

Referring to the drawing, a cylindrical glass tube or capillary tube 1,both ends of which have been fused, contains a Luminophor inside, forinstance zinc sulfide, which has been applied as an inside wall coating,or placed into the tube as a powdery substance, and as well as aradio-isotope which is gaseous at room temperature, for instance saidradio-isotope may be Tritium or Krypton, which develops a pressure thatis below ambient atmospheric pressure.

Glass tube 1 is provided with an outside diameter in the range of 0.5 to10 mm. and an original length of, for instance, one meter. The glasstube 1 is held at both of its ends by clamping devices 2 and 3. Clampingdevice 2 holds the glass tube during the whole process of subdividing byfusing, the glass tube being progressively movable in steps in thedirection of arrow 4 by devices (not shown in detail). Clamping device 3can be detached radially from the glass tube 1 in the direction of arrow5, and clamp 2 may be fixed or displaceable as desired.

Laser 6 shown in block configuration, the output beam 7 of which isdirected to glass tube 1, is disposed laterally and preferably normal tothe glass tube 1. A focusing device 8, and/or a device for controlingthe output beam 7 such as a Kerr cell or crossed prisms shown in blockconfiguration sets up a parallel Laser beam 9, which is directed towardthe glass tube 1 at the point to be fused and said Laser beam 9 at thatstage having about the same cross section as the glass tube. Laser beam9 need not necessarily be parallelly directed but it can also have aconvergent course. The diameter of the beam as it reaches the tube whichis to be divided is preferably approximately as large as that of thetube. The purpose is to fuse enough glass to form the new sealed ends ofthe two tubes produced. The beam should be closely localized to thedesired area to minimize waste of energy, and to avoid flow of heat toadjacent areas of the tube since this would deactivate the Luminophor inadjacent areas.

Alongside Laser beam 9, a metal plate 10 has been fitted, which can beoscillated (LP) swung in and out to and from the solid and dotted lineposition in the figure. In the position illustrated in solid line, metalplate 10 does not affect Laser beam 9, so that the latter can strikeglass tube 1 unimpeded. In the position shown in a dotted line, metalplate 10 lies at an angle of about 45 in the Laser beam and deflects thelatter by reflection by about from the normal parallel direction ofLaser beam 9.

As shown in the drawing, opposite and spaced beam Laser 6 and from Laser6 to glass tube 1, a metal reflector 11 is provided which reflects backpassing rays of Laser beam 9, to the zone of the glass tube being fusedand thereby makes possible a substantially complete utilization of theenergy of the Laser beam 9 as well as a symmetrical effect of the Laserbeam on the glass tube.

Laser 6 generates a beam whose wave length range lies in the optimumabsorption range of the glass material of the glass tube, that is in theinfrared spectral range. Laser 6 can for instance in C0, Laser unitdevelop and operate with a beam wave length of 10.6 and about Wattoutput.

Furthermore, devices (not shown) can be present for rotating glass tube1 in the direction of arrow 12 during the fusion process. When thereflector 11 is provided, it may be unnecessary to turn the glass tubeto assure uniform heating of the fusion point of the glass tube. It mayalso be expedient to provide further devices (not shown), which may forinstance act on clamping device 3, for the purpose of pulling apart theformed glass tube parts from each other in the direction of the arrow 13during the fusion process of the respective glass tube sections.

Finally, it is advantageous to provide corresponding associated controland operating devices, in order to carry out the process ofautomatically subdividing the glass tube into fused (melted-down) glasstube sections by means of a Laser beam. The operating sequence of thissubdividing process is the following:

When Laser 6 is in continuous operation, that is when Laser beam 9 iscontinuously generated, metal plate 10 is at first in the swung-inposition and deflects Laser beam 9 from glass tube 1. Glass tube 1 isgrasped from both sides and is placed in such an axial position that,between the left-side end of the glass tube, which has already beenfused, and the desired position of the Laser beam 9, and the desiredlength of glass tube section to be fused, i.e., to be cut off, isattained. Thereupon, if desired, while simultaneously turning glass tube1, the metal plate is swung out, so that Laser beam 9 strikes the glasstube 1 unimpededly and instantaneously heats the tube at the desiredzone and causes it to fuse at the point of impact. As soon as thesuccessive ends of the fused glass tube section which have beenseparated, the remaining portions of glass tube 1 are successivelyfused, all of which takes but a few seconds. For this purpose, a pullcan be applied on the untreated section of glass tube in the directionof arrow 13, and the metal plate 10 again swung into the Laser beam 9.

Thereupon glass tube 1 is advanced by the length of the section desiredin the direction of arrow 4, and is grasped again adjacent the fused endby means of clamping device 3, whereupon the fusion process along thelength of the remainder of the supported glass tube is repeated in themanner described.

During the process of subdividing the glass tube with the Laser beam,the glass material of the glass tube 1 becomes more fluid at the fusingpoint than by working therein with a flame. in this manner, a series ofuniformly round, fused ends of subdivided sections of the glass tube isobtained, so that the work of finishing the ends with a flame, which isotherwise usually necessary under prior procedures, can be dispensedwith.

By means of the Laser beam an instantaneous, intense and closelylocalized heating up of the glass tube is obtained, so that theremaining other parts of the length of glass tube to be separated intosections is heated up only slightly. Accordingly, the separated glassbody sections do not exhibit at its ends undesirable dead zones withrespect to illumination power.

Since there is produced only a slight heating effect on the glass tubesections being and to be separated, there is also only a very slightincrease in pressure of the radioactive gas contained in the glass tube.This makes it possible to maintain the difference in pressure of the gasin the tube wjtg respect to atmospheric ressure a a low figure whicgives rise to an optimal y Intense brightness of the radioactive lightsource therein.

A further advantage of the process described lies in the fact that theLaser beam can be regulated and controlled with ease and precision, sothat instantaneous heating of the glass tube, uniform in each meltingprocess, can be obtained, while all the disadvantages of an open flame,which heats up the surroundings are eliminated.

The process described is, therefore, especially suitable forautomatically and economically radioactive light sources, whichconstitute separated sealed fused sections by means of subdividing along glass tube, incorporates the Luminophor and radioisotopes, saidradioactive capillary light sources being for instance of 10 mm length,and which glow uniformly over their entire length.

What is claimed is:

l. A process of dividing a long, sealed glass tube containing aLuminophor and a radioactive gas at subatmospheric pressure into ashorter sealed tube suitable for use as a light source and a sealedremainder, comprising the step of heating said long, sealed glass tubeto fusion with a closely localized Laser beam at the zone whereat saidlong, sealed, glass tube is to be divided so that a sufficient quantityof glass is drawn in from the side wall to form end walls, to dividesaid long sealed tube and to simultaneously seal the ends of the twotubes produced without the loss of radioactive gas by drawing inwardlyglass fused by said beam, said inward movement of said fused glassresulting, at least in part, from said pressure within said glass tubebeing subatmospheric.

2. A process as defined in claim 1, and including the steps of rotatingsaid glass tube during heating with said Laser beam and advancing saidlong, sealed glass tube axially past the Laser beam by an amountessentially equal to the length of the next of the shorter tubes to bedivided from said remainder subsequent to dividing the previous shortertube from said remainder.

3. A process as defined in claim 1, including the step of drawing apartsaid remainder and said shorter tube during the heating with said Laserbeam.

4. A process in accordance with claim 1 including the step of deflectingthe Laser beam by means of reflection from a metal plate after eachfusion of a glass tube section of the glass tube.

5. A process in accordance with claim 1, including the step ofreflecting back to the glass tube being fused those rays which passbeyond said tube.

6. A process in accordance with claim 1 wherein the Laser beam as it isfocussed at the zone on the glass tube which is to be fused said Laserbeam has approximately the same cross section as the glass tube.

# i I Q i

1. A process of dividing a long, sealed glaSs tube containing aLuminophor and a radioactive gas at subatmospheric pressure into ashorter sealed tube suitable for use as a light source and a sealedremainder, comprising the step of heating said long, sealed glass tubeto fusion with a closely localized Laser beam at the zone whereat saidlong, sealed, glass tube is to be divided so that a sufficient quantityof glass is drawn in from the side wall to form end walls, to dividesaid long sealed tube and to simultaneously seal the ends of the twotubes produced without the loss of radioactive gas by drawing inwardlyglass fused by said beam, said inward movement of said fused glassresulting, at least in part, from said pressure within said glass tubebeing subatmospheric.
 2. A process as defined in claim 1, and includingthe steps of rotating said glass tube during heating with said Laserbeam and advancing said long, sealed glass tube axially past the Laserbeam by an amount essentially equal to the length of the next of theshorter tubes to be divided from said remainder subsequent to dividingthe previous shorter tube from said remainder.
 3. A process as definedin claim 1, including the step of drawing apart said remainder and saidshorter tube during the heating with said Laser beam.
 4. A process inaccordance with claim 1 including the step of deflecting the Laser beamby means of reflection from a metal plate after each fusion of a glasstube section of the glass tube.
 5. A process in accordance with claim 1,including the step of reflecting back to the glass tube being fusedthose rays which pass beyond said tube.
 6. A process in accordance withclaim 1 wherein the Laser beam as it is focussed at the zone on theglass tube which is to be fused said Laser beam has approximately thesame cross section as the glass tube.